1. Field of the Invention
The invention relates to the field of tissue reconstruction and in particular to electroforming tissue and cartilage in particular.
2. Description of the Prior Art
Cartilage serves many functional and structural roles in the head and neck, including the support of soft tissue in the ear and nose, maintenance of airway patency, phonation, and joint movement. The functional and esthetic defects in the head and neck that result from cancer surgery, trauma, or congenital malformations have led to the development of surgical techniques to reshape cartilage to recreate damaged or absent structures.
Conventional reconstructive techniques (e.g., otoplasty, rhinoplasty, tracheoplasty) involve the grafting or shape modification of autologous cartilage (harvested from the ear, nasal septum, or rib). Currently, the graft is carved, sutured, and/or morselized to recreate the shape of the absent tissue and, as a consequence, abundant normal healthy cartilage tissue is discarded. These techniques also in general require surgical exposure of the tissue to provide direct access to the graft tissue. Further manipulation of tissue in this fashion creates focal injury to the extracellular matrix. Because only a limited amount of cartilage is available from donor sites, conventional reconstructive techniques may lead to significant donor site morbidity. Similarly, some cartilaginous malformations in the head and neck are treated using surgical techniques that do not require grafting (e.g., rhinoplasty, laryngoplasty), but rather reshaping pre-existing cartilage structures in situ using the aforementioned traditional reconstructive techniques. These techniques have the same limitations as grafting techniques, and also require open/invasive (non-endoscopic) surgical approaches that frequently result in undesirable, irreversible tissue changes and complications that may require revision surgery, and possibly additional cartilage grafting.
Current reconstructive techniques include carving, morselizing, scoring, or suturing native cartilage grafts. The disadvantages of these approaches include donor site morbidity from graft harvest, waste of excess graft tissue, shape memory effects, and lack of control over warping, particularly in costal cartilage tissue.
Several alternative approaches to reshaping cartilage have been advocated, including enzymatic digestion in situ, radiofrequency (RF) reshaping, and laser cartilage reshaping. Of these approaches to changing the shape of native cartilage tissue, laser reshaping has received the most attention. In 1993, Helidonis et al. “Laser Shaping Of Composite Cartilage Grafts”. Am J Otolaryngol 1993;14: 410-412, proposed an alternative laser assisted approach based on thermal-mediated stress relaxation to reshape cartilage. Despite clinical uses of laser technology to reshape human cartilage, this method remains investigational, and the associated biophysical changes accompanying shape change are incompletely understood.
Recently several new techniques have been developed and/or investigated including electroforming, thermoforming (laser and RF), and enzymatic reshaping. In each of these cases, the intrinsic forces in tissue which resist deformation are relieved or balanced by accelerating stress relaxation, albeit the molecular mechanisms of action may be different in each case. During the reshaping process, internal stress decreases over time, and this is the most important physical process to monitor during any shape change procedure. Internal stress measurements are very difficult to perform and require the application of strain gauge type devices to measure either stress or strain.